1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to data processing systems including multiple processors for which it is desired to control the performance.
2. Description of the Prior Art
It is known to provide multi-processing systems including a plurality of processors operating to execute respective streams of program instructions. Examples of such multi-processing systems are SPARC computer systems, IBM370 computer systems and, multi-processor personal computers running multi-processing aware operating systems such as Windows XP. The use of multi-processing is conventionally associated with high performance systems in which it is desired to execute a large number of program instructions in a small amount of time. Thus, multi-processing systems tend to be associated with mainframe computers, servers, high performance workstation computers and high performance personal computers. Within such systems it is normal to provide multiple processor cores each operating at their maximum possible clock speed and executing respective streams of program instructions.
In contrast to the high performance multi-processing environments discussed above, it is also known to provide uni-processing systems which utilise selectable clock speeds so as to reduce energy consumption. Known examples of such systems are the Speedstep processors produced by Intel Corporation, the Crusoe processors operating under control of Longrun software as produced by Transmeta Corporation and the Intelligent Energy Management systems produced by ARM Limited. In these systems the clock speed and operating voltage level is adjusted between different settings. At a lower clock speed and with a lower operating voltage the processor is capable of executing fewer instructions in a given period of time, but consumes significantly less power. This is an important advantage in power constrained environments, such as portable computing devices. Thus, it is possible with implementations of the Speedstep processors to detect whether or not a portable computer is currently connected to a mains power supply or is operating on a battery power supply. When operating on a battery power supply a lower clock speed and a lower operating voltage is used by the processor core to reduce the specific energy consumption in relation to the program instructions executed. The Longrun software and IEM system provides a more sophisticated degree of control over the processor core in that the processor core may be switched between several different clock speeds and operating voltage levels in dependence upon the detected processing workload of the processor core at that time such that when the workload is low the processor core is switched into a low specific energy consumption configuration and when the workload is high the processor core is switched into a configuration which consumes more energy, but yields higher processing performance.